Fetal hypoxia is a leading cause of fetal morbidity and mortality. The ability of the fetus to adapt to hypoxic stress is critical for its survival. Nitric oxide (NO) plays an important role in cardioprotection as an important modulator of both coronary flow and cardiac contractility, and gene expression of NO synthase (NOS) is hypoxia-sensitive. We hypothesize that chronic hypoxia upregulates the NOS pathway in fetal hearts inducing cardioprotection by increasing eNOS-derived NO in the coronary circulation and cardiac injury by iNOS-derived NO in the cardiomyocytes of the ventricle. To test this, pregnant guinea pigs will be exposed to chronic hypoxia (10.5%O2 for 14d duration) and hearts of fetuses will be examined in 5 specific aims: Aim 1) To test the hypothesis that chronic hypoxia increases coronary and cardiac gene expression of NOS and angiogenesis in the fetal guinea pig heart. Gene/protein expression of the NOS/cGMP/PKG pathway will be quantified and proteins localized using immunofluorescence in normoxic (NMX) and hypoxic (HPX) fetal hearts. Aim 2) To test the hypothesis that chronic hypoxia induces cardiac injury in the fetal guinea pig heart. Apoptosis (Bax/Bcl2 expression, TUNEL) and coronary angiogenesis (VEGF, VEGFR1, VEGFR2, Ang1, Ang2 expression) will be quantified and functional responses of coronary flow and contractile force measured in isolated fetal heart preparations. Aim 3) To test the hypothesis that in utero inhibition of iNOS-derived NO and ROS generation protects the fetal heart from hypoxia-induced injury. NOS and ROS inhibitors will be administered to pregnant mothers and the in utero effect on fetal heart gene expression and coronary/contractile function measured. Aim 4) To test the hypothesis that iNOS-derived NO stimulates ROS generation in isolated fetal cardiomyocytes (FCM). The mechanism of iNOS-derived NO in stimulating ROS will be studied in cultured FCM derived from NMX and HPX fetal hearts. Aim 5) To test the hypothesis that prenatal hypoxia increases arterial blood pressure in the guinea pig offspring via the iNOS pathway. Radiotelemetry of blood pressure and cardiac gene expression/functional responses of hearts of age-matched offspring will be measured. We propose that hypoxia alters NOS expression in the fetal heart contributing to adaptive and maladaptive responses, both pre- and postnatally. This will identify iNOS-derived NO synthesis as a target pathway for fetal survival.